The present invention relates to a method and regulating system for regulating the air/fuel ratio fed to an internal-combustion engine. An internal-combustion engine of this type may comprise any internal-combustion engine which is known in the prior art, such as a diesel engine or spark-ignition engine, which may operate using either the two-stroke or the four-stroke principle.
The authorities are imposing ever higher demands on emissions from such engines. One of the emission criteria which is of importance is the NO.sub.x, level.
In engines which operate with a known, constant fuel quality, regulation of this nature is comparatively simple to carry out. A so-called lambda sensor is arranged in the exhaust duct and measures the amount of oxygen present. On this basis, the air/fuel ratio can be regulated with the aid of a feedback system.
However, as soon as the calorific value of the fuel fluctuates, a system of this nature has proven to be no longer satisfactory. For example, if an amount of non-combustible gas, such as a gas which reduces a combustion temperature, such as CO.sub.2, is fed to a gaseous fuel, the oxygen content in the exhaust gas will change, and a device of this nature will endeavour to make such a mixture leaner by equalizing the oxygen content again. Such a reaction is undesirable. Therefore, it is proposed in the prior art to control the air/fuel ratio in engines which operate under fluctuating conditions in a different way. Examples of how to do this are given in European Application 0,259,382 A in the name of Jenbacher Werke and European Application 0,727,574 A, in the name of Deltec Fuel Systems B.V.
In both cases, the combustion engine is used to drive a generator, and the electric power generated is used as an input for air/fuel regulation. In European Application 0,259,382 A, the pressure in the inlet manifold of the internal-combustion engine is measured and an optimized inlet manifold pressure is determined on the basis of the generator power which is generated. These two inlet manifold pressure values are compared with one another and correction is carried out if necessary.
In European Application 0,727,574 A, the desired efficiency of the engine under operating conditions is determined and compared with the actual efficiency. The efficiency, on the one hand, is a constant value and, on the other hand, is determined from the power of the engine. If there are differences between the measured efficiency and the calculated efficiency, correction is carried out.
For both applications, it is essential that there should be a power output signal.